The present invention relates to a process for fixing wound items, in particular wire windings in electrical equipment, such as rotors, stators and transformers by impregnation (for example dipping or trickling) with radically polymerisable compositions. The invention also refers to radically polymerisable compositions usable for the process.
Electrical equiment, such as rotors, stators or transformers often consist of metal core around which a foil or wire material, for example a copper foil or wire is wound. The windings in these three-dimensional components are currently impregnated with radically polymerisable compounds and then cured in order to fix the wound items and to maintain their function. Curing is achieved by application of heat at temperatures of above 100.degree. C. in an oven or by inductive heating.
The radically polymerisable compounds, known as impregnating resins or agents, contain for example unsaturated polyester resins which are dissolved in unsaturated aromatic or aliphatic radically polymerisable monomers, such as for example styrene or hexanediol diacrylate. Such monomers often have a very high vapour pressure, such that a large proportion thereof escapes during thermal curing. This gives rise to environmental problems; the materials containing styrene have, for example, an unpleasant odour and relatively high toxicity. Disposal, for example by subsequent burning, is thus necessary.
It is also known that the heat necessary for curing is produced by applying an electrical current to the electrically conductive windings after their impregnation and current conduction then produces the necessary temperatures. This leads to curing of the impregnating resins on end in the wire windings.
However, the wound items also contain solid parts, though which no current flows. The impregnating resin is not solidly cured on these parts. Therefore, it is additionally necessary to cure the components in an oven.
It is furthermore described in DE-A-40 22 235 to coat electrical wound items with radically polymerisable impregnating agents and, in order to prevent the vaporisation of substances hazardous to health, to crosslink the surface with UV radiation. This produces a cured surface and the low molecular weight polymerisable substances below the surface can no longer pass into the vapour phase on thermal crosslinking. However, in order to achieve crosslinking, this process requires subsequent energy intensive heat treatment in an oven. A similar process is described in DD 295 056.